The present invention relates to a method, and an apparatus desirably practicable therefor, of manufacturing long bars, such as round bars, square bars, and flat bars, with or without tapered portion, by means of a multi-tandem type roller dies means in which the roller gap thereof is controlled by roller adjusting means.
A set of roller dies is usually composed of a plurality of idler rollers disposed in a close approach at the outer periphery of each roller for processing a work through a pass or die hole formed by a concave groove made on the outer periphery of each roller, while the work is given a propelling force by means of a drawing means. This type process employing roller dies is said to be characteristically advantageous in its far lesser frictional resistance and far larger reduction percentage or reduction of area per one pass (for example 40% per one pass) in comparison to the ordinary process using a drawing die.
The multi-tandem type roller dies means having more than one set of such roller dies in succession is widely known as effective in realizing the above-mentioned advantages.
However, the roller dies means of the conventional type has, on one hand, a weak or vulnerable point in its difficulty of adjusting the roller gap. Known remedies for the problem of roller gap adjusting are a disposition of a tapered roller chock for protruding (inserting) or retracting a tapered liner placed between the pair of roller chocks sustaining the rollers, and a disposition of a roller adjusting screw for adjusting the roll position.
In those accessory adjusting devices, equal amounts of adjusting for each roller of each set is said to be difficult, and a possible up- and down fluctuation of axis or center of the pass defined by the concave grooves on the rollers may produce a bending of the works or the processed articles and a hitch in obtaining works of desired shape. Furthermore, adjusting the roller gap while the process is progressing is said to be next to impossible.
In the cold-rolling of thin plate many devices for controlling the roll gap of the rolling mills are proposed, most of which being ones for adjusting the roll gap by the movement of only one roll, not on both sides. Rolling is usually performed by a driver roll or rolls, so the reduction percentage in the process is low, usually less than 10 percent per one pass. It necessitates installation of several sets of rolling mills in succession for getting the desired percentage of reduction, resulting a bulky equipment and high cost.
In the event of incorporating such roll gap adjusting devices into a well known roller dies means, the gap adjusting by means of movement of a roller, only on one side, is liable to cause a shifting of processing center, an axial line of the work processed, bringing about bending of the work and difficulty of finishing the work in desired dimension and shape, which tendency particularly conspicuous in the roller dies because of its large reduction of the area in each pass.
In recent years demand for tapered bars has been increased for the purpose of improving the performance of, and attempting the lightening of, construction materials. In addition, tapered bars of gradually varied diameter have been put into practice, for use as suspension coil springs for vehicle, because of the advantageous feature of variable spring constant in accordance with the load.
A method for manufacturing tapered bars of high dimensional precision in large quantity and on economical basis has never been developed. It is therefore a common practice to produce such tapered bars by machining, irrespective of its poor economy. Mass productive and an economical way of manufacturing tapered bars has been sought in various quarters.